Corundum phonograph needle and sound reproducing apparatus embodying same



Dec. 4, 1951 Filed July 18, 1947 J. F. PELTON ET AL CORUNDUM PHONGGRAPHNEEDLE AND SOUND REPRODUCING APPARATUS EMBODYING SAME INVENTORS JOHN F.PELTON BY THOMAS F. HART ATTORNEY Patented Dec. 4, 1951 'CORUNDUMPHONOGRAPH NEEDLE AND SOUND REPRODUCINQ APPARATUS r nvn BODYING SAMEJohn F. Pelton, Kenmore, and Thomas F. Hart, ..Bufialo, N. Y.,assignors, by mesne assignments, to Union Carbide and CarbonCorporation, a

corporation of New York Application July 18, 1947,,Serial No. 761,812

This invention relates to extending the playing lives of unicrystallinecorundum phonograph needles, especially needles of the composite typewherein a. small unicrystalline corundum point is secured in the end ofa shank of different material, such a metal or plastic.

Composite phonograph needles having unicrystalline corundum points, suchas natural or synthetic ruby and sapphire, have been used extensively inrecent years. Because of their great hardness such needles theoreticallyshould have extremely long playing lives. It has been found, however,that ruby and sapphire needle points are quite erratic in behavior, somehaving relatively long lives and others failing in service after onlyrelatively short periods. When premature failure occurs it is usually bythe spalling or chipping of particles from the needle points ratherthanby ordinary abrasion. This problem has been of considerable concernin the art of sound transcription, but attempts to solve it met withlittle success prior to the present invention. The principal object ofthis invention is to extend and make more uniform the playing lives ofphonograph needles having unicrystalline corundum points.

In the drawing Fig. 1 is a schematic perspective view showing a corundumphonograph needle point in playing position on a phonograph record, thesize of the needle point being considerably exaggerated;

Fig. 2 is an enlarged side elevational view, parts being in section, ofa composite phonograph needle mounted in playing position in aphonograph tone arm; and

Fig. 3 is an enlarged front elevational view of the phonograph needleshown in Fig. 2. We have found, surprisingly, that the life of acomposite sound reproducing needle N having .a unicrystalline corundumpoint II can be lengthened considerably by properly positioning theneedle on a laterally modulated record R so that two conditions areobserved with reference to the crystallographic c-axis cc of the needlevis in contact with the record (approximately nor-v mal to the recordradius) a .As a practical commercial matter, it is not 8 Claims. (01.274-38) possible to fulfill both of the above conditions perfectly onall needles, but a variation of plus or minus 15 degrees in either orboth conditions. can be tolerated without sacrificing much in theuniformity and extent of life of the needles.

The necessity for observing both of .the abovedescribed conditions-isemphasized by the following results of a series of accelerated lifetests. conducted on a large number of. composite needleswith sapphirepoints mounted in metal shanks and carried in a tone arm'which exerted aneedle force of 1% ounces on dis-c type record R.

A. Of the needles which were so mounted that both of the above describedconditions No. 1 and. N0. 2 were observed Within plus-or minus .15degrees, 88%-were still in satisfactory condition after 300 minutes ofplaying time.

B. Of the needles which were so mounted that. the c-axis cc'wasapproximately parallel to the record within plus or minus 15 degrees(condition No.1), but that the cg plane was inclined at an angle of morethan 15 degrees to the tangent to the record groove, only. 50% werestill in satisfactory condition after 300 minutes of playing,

time...v

C. Of the needles which were so mounted that. thecg plane wasapproximately tangent to.the record groove within plus or-minus 15degrees (condition No. 2), but that the c-axis ccwas inclined at anangle of more than 15 degrees to. the record, only 30% were still insatisfactory condition. after 300 minutes of playing time.

D. Of the needles which were so mounted thatv neither of the abovedescribed conditions No.1 and No. 2 was observed within plus or minus 15degrees, only 10% were satisfactory after 3.00 minutes of playing time.Many of the unsatisfactory needles failed after much less than .300.minutes, in several instances lasting for less than 30 minutes.

In all of the above tests, the points of the un-. satisfactory needleswere too badly chipped or spalled to be used longer.

Deviations of the c-axis cc and the cg plane of morethan 15 degrees fromone or both of the two critical conditions No. l and No. 2 cause asudden large decrease in the percentage of satisfactory needles. Forexample, of a group ofneedles wherein the deviation from the optimum ofone orboth conditions was between 15 and .30 degrees (but neithercondition greater than 30. degrees) only 67% were satisfactory .in lifetests comparable to those described above.

It is apparent that on an extra large disc type record or on a recordwheretheradius of the rec,

6rd groove is infinitely large, for example a recording tape, tangencyof the ca plane to the groove is then for practical purposes identicalwith parallelism to the groove and condition No. 2 is fulfilled bypositioning the needle point so that-thefcg plane is parallel to therecord groove.

The average user of phonograph needles has no facilities for determiningthe position of the c-axis in a corundum needlepoint. Tomake availableto the public the advantagesofour in" vention, therefore, it isessential for the manufacturer of phonograph needles tomount the table23 when the point is aligned with the edge,

ing-of the needlepoint when a. record is placed on corundum needle pointII in ashank l fi inisuch a way that conditions No. 1 and N612 iwillneces sarily be observed by the ultimate consumer when he mounts theneedle in his tone, arm or pick-up T. This is done by providing eachneedle FT with a suitable index so disposed with reference to the cgplane of the point II and the c-axis direction of the point that whenthe needle is positioned in a phonograph tone arm with the index in aposition determined by a prearrangedcode of instructions the cg plane isapproximately tangent to the groove or sound track 13 of a record R. tobe played,- and the c axis c-'-c of the point is approximately parallelto the record. Any suitable index may be used, for example anindentation, a surfacemark, or a hole;

A convenient andv practical index is the set screw seat of the needlewhich generally is a flattened side of the needleshank as shown'at H inFig. 2. In most modern phonographs the needle set screw 19 is locatedhorizontally in the extreme end of the tone arm '1,- and theneedlesOcketZl" is iinclinedat' an angle of about 65 to the record R, inthe direction of record rotation. In most cases, therefore, the properpositioning of the needle is assured when the corundum point II is soset in the lower end of shank that the airplane of the pointapproximately bisects the set screw seat H, as shown in Fig. 3, and thec-axis cc' forms an angle of about 65" with the longitudinal aXisL-L ofthe top'portion ofshank I5 on the side of the longitudinal axis remotefrom set screw seat H.

Manyrdifferent shapes of set screw seats can be used, such as flat;concave, grooved; or V shaped. However, the usual set-screw seat is fiatas shown at I1, so that the proper setting of most needle points intheir shanks requires that the cg plane be approximately normal to sucha flatseat;

When an index as described above-isprovided, proper positioning of theneedle point on the'rec-" 0rd is independent of the needle shape. Bothstraight needles and needles having simple and complex curvatures can bepositioned-properly.

In the case of the popular S=shaped needles,

.such as the needle N illustrated in Fig. 2,-the

plane of the S-curve is normallymaintained approximately tangent to therecord groove l3 when the needle is in playing position. Iii such aneedle the advantages of the present invention are provided by sosetting point 1| in shank [5 that the cg plane approximately parall'elsthe plane of the S-curve and the .c-axis c c lies at about to thelongitudinal axis IJI3 of the upper portion of shank 15 on the-sideofaxis and the c -axis cc is approximately parallel to the top of theturntable. Thus, proper positiontne turntable is assured.

We'claim: V I .A .phonog'raplii needle comprising a shank -having a= set'screwseat on a side adjacent the top thereof? and a unicrystallinecorundum point carried-by said shank at the bottom thereof, said pointbeing so positioned that the co plane of said point approximatelybisects said seat, and that the c-axis of said point and thelongitudinal axis of the top portion of said shank form an angle ofabout 65 with one another on the side of said longitudinal axisremotefrom said seat.

.2; A g phonograph needle comprising 7 a shank having affla't set screwseat on a side thereof adjacent the top thereof; and a unicrystallinecorundum point carried by said shank at'the bottom thereof, said pointbeing so positioned that-the cg plane of said point is approximatelynormal to said flat seat, and that the c-axis of said point and thelongitudinal axis: of the top portion of said shank form anangle ofabout 65 with one another on the side of said longitudinal axis remotefrom said flat seat.

3; A phonograph needle comprising a'shank' having a plane S curve, and aunicrystalline corundum point carried by said shank at the bottomthereof, said point being so positioned that-the cg plane of saidpointparallels the plane of said S-curve, :and that the c-axis of saidpoint and the longitudinal axis of the top portion of said shank form anangle of about 65 with oneanother onthe side of said longitudinal axisremote from said point.

4-. A phonograph needle comprising a shank having a top for insertion inthe tone armof a; phonograph and a unicrystalline co'rund'umpoint at thebottom of said shank, said needle having anindex thereoniso disposed.-with reference; to ithe cg. plane of said' pointand the c'-'axispOSition of said point that when said-needle is post; tioned in aphonograph tone arm with said index in a'position determined by. a'prearranged code, the cg plane of' said point is approximately tangentto the sound track of a record to be played; and'the e-axis of saidpoint is approximately parallel to'such record. I

5.-In a phonograph having a'rotatable record table and a tone arm havinga needle socket, a needle adaptethto cooperate with a record onsaidtable, saidneedle comprising a shank extending'upwardly. into saidsocket and a uni-; crystalline corundum point at the bottom of saidshank,- said point being so positioned that the 6- axis thereof isapproximately parallel to said tableand that the co plane'of said pointis approximately tangent to the edge of'sa'id table; when said point isaligned with said edge.

6; In sound reproducing apparatushaviiig a. phonograph record providedwith'a' sound track, a unicrystalline corundum phonograph needle"hailing a pointriding in said sound track thecg plane or said needlebeingapproximately tangent: to said sound track at the pointercontac'tfiofi said needle .with' saidrecord; the .oi-axis of said needlebeing approximately parallel to said rec--l rd.

7. In sound reproducing apparatus having a' rotatably mounted disc typephonograph record provided with a spiral sound track, a unicrystallinecorundum phonograph needle having a point riding in said sound track,the cg plane of said needle being approximately tangent to said soundtrack at the point of contact of said needle with said record, thec-axis of said needle being approximately parallel to said record.

8. In a phonograph having a rotatable record table and a tone armcarrying a needle adapted to cooperate with a record on said table, saidneedle comprising a unicrystalline corundum point, the cg plane of saidpoint being approximately tangent to the edge of said table when saidpoint is aligned with said edge, and the caxis of said point beingapproximately parallel to said record.

JOHN F. PELTON. THOMAS F. HART.

3 REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,737,253 Linsell Nov. 26, 19292,265,601 Imelmann Dec. 9, 1941 2,276,562 Capps Mar. 17, 1942 2,320,416Dally June 1, 1943 2,328,889 Capps Sept. '7, 1943 2,346,733 Dally Apr.18, 1944 2,355,877 Le Van Aug. 15, 1944 FOREIGN PATENTS Number CountryDate 751,047 France Aug. 25, 1933 duction Reaches Commercial Scale in U.S., October, 1943. (Four pages. Copy in Division 5.)

